1. Field of the Invention
The present invention relates to an encoding apparatus and method for error correction which is applied to record, for instance, audio PCM signals onto a magnetic tape by rotary heads and, more particularly, to an apparatus and method for error correction which is provided in a digital encoder to record high quality audio PCM data, as disclosed in U.S. Pat. No. 4,551.,771.
2. Description of the Prior Art
There is a known error correction encoding apparatus and method for use with information symbols arranged two-dimensionally in a matrix form in which encoding processes of error detection and error correction codes, e.g., Reed Solomon codes are executed in each of the vertical and lateral directions of the information symbols. These codes are transmitted for each column in the vertical direction. On the reception side, the error correction is performed by using a first error detection code and a first error correction code and, at the same time, a pointer indicative of the presence or absence of errors is formed. Next, the errors are corrected by a second error detection code and a second error correction code with reference to this pointer.
In the case where the foregoing error correction encoded data is transmitted for each column, a sync signal and sub-data such as a block address and the like are added to thereby form one block of data. For example, in U.S. Pat. No. 4,630,272, there is shown a method whereby a sync signal and an address in which error detection can be independently performed by a CRC code are added to each column of data and to the parity data of a first error correction code, thereby forming one block. In the above U.S. Patent, as shown in FIG. 1A herein, for the address, the error detection can be executed by the CRC code and for a data portion (PCM audio signals), encoding processes of a first error correction code (referred to as a C1 code) and a second error correction code (referred to as a C2 code) are performed. In the case of the encoding by FIG. 1A, however, since the C1 code is not applied to the address, the protection against errors is insufficient.
To solve this problem, for example, as disclosed in U.S. Pat. No. 4,682,332 and as shown herein in FIG. 1B, an error correction encoding is proposed in which an encoding by a C1 code is also executed for the address.
When a header consists of only an address, the error correction encoding shown in FIG. 1B is useful. However, if PCM audio signals (main data) are included in the header in addition to the address, the encoding by the C1 code is only executed for the main data and there is a problem in that the protection for errors is insufficient for a reason to be mentioned later. Encoding by the C2 code of the whole header, including the address, to eliminate this drawback causes an inconvenience in that the data area in which the addresses are recorded is lost by the existence of the C2 parity.
To solve such a problem, the applicant of the present patent application has proposed an error correction encoding apparatus in which a whole header together with a data portion is C1 encoded and the encoding of a C2 code is performed for the main data included in the header, excluding addresses, thereby enabling error protection the part of the main data included in the header to be made strong, so that the main data can be recorded into the header part. This error correction encoding apparatus is suitable when it is used in what is called an 8-mm VTR as disclosed in U.S. Pat. No. 4,551,771 in which both a video signal of one field and audio PCM signals of one field, i.e., time base compressed audio PCM signals are recorded on a magnetic tape by a single scan.
In the already commercialized 8-mm VTR, a sampling frequency of the audio PCM signals is selected to be 2f.sub.h (f.sub.h : horizontal frequency). Therefore, the rotary heads which rotate at a frame frequency and a sampling system are synchronized, and the problem of asynchronization between an image and an audio sound does not occur. However, there is a problem in that the sampling frequency of the conventional 8-mm VTR is too low with respect to a point that audio signals of a high quality are recorded and reproduced. In addition, there is a problem of the absence of matching with the sampling frequencies (44.1 kHz, 48 kHz, 32 kHz, etc.) which are used in other digital audio apparatuses such as CD players and rotary head type digital audio tape recorders (R-DATs). Therefore, it is preferable to be able to use those frequencies (44.1 kHz, 48 kHz, 32 kHz, etc.) as the sampling frequency of the audio PCM signals in the 8-mm VTR.
However, since there is no integer ratio relation between the above-mentioned frequency and, e.g., the field frequency (59.94 kHz) of the NTSC system, the number of sampling data included in one field period is not an integer. Therefore, when both a video signal and audio PCM signals are recorded on the same track, as in the 8-mm VTR, the problem occurs of asynchronization between the video image and the corresponding audio sound.